This invention relates to polymerizable dental resins for dental composite materials and the method of manufacture of such resins for restorative dentistry, and more particularly to dental composite materials that are useful as crown and bridge materials either with or without an alloy substrate, as reconstructive materials, restorative materials, filling materials, inlays, onlays, laminate veneers, dental adhesives, cements, sealants and the like. This invention also relates to dental composite materials that are useful as surface sealants and glazes for dental restorations.
In recent years, materials used for dental restorations have principally comprised acrylate or methacrylate resins, hereinafter “(meth)acrylate” resins. Typical (meth)acrylate resin materials are disclosed, for example, in U.S. Pat. No. 3,066,112 to Bowen, U.S. Pat. No. 3,194,784 to Bowen, and U.S. Pat. No. 3,926,906 to Lee et al. An especially important methacrylate monomer is the condensation product of bisphenol A and glycidyl methacrylate, 2,2′-bis[4-(3-methacryloxy-2-hydroxy propoxy)-phenyl]-propane (“Bis-GMA”). Alternatively, Bis-GMA may be synthesized from the diglycidyl ether of bisphenol A and methacrylic acid (see U.S. Pat. No. 3,066,112 to Bowen).
Because the wear and abrasion characteristics and the overall physical, mechanical, and optical properties of these unfilled (meth)acrylate resins is poor, and because (meth)acrylate resin systems exhibit high coefficients of thermal expansion relative to the coefficient of thermal expansion of the tooth structure, these substances by themselves are less than satisfactory. In particular, the disparity in thermal expansion coupled with high shrinkage upon polymerization results in poor marginal adaptability, and ultimately leads to secondary decay. Composite (meth)acrylate dental restorative materials containing (meth)acrylate resins and ceramic fillers were thus developed. These filled compositions are useful for a variety of dental treatments and restorative functions including crown and bridge materials, fillings, adhesives, sealants, luting agents or cements, denture base materials, orthodontic materials and sealants, and other dental restorative materials. Despite their suitability for their intended purposes, however, many of these materials have shrinkages of about two to about 4% by volume upon polymerization.
Alternative resinous materials include the ring-opening polymerization of epoxides. These resins have lower shrinkage than methacrylates, but exhibit compatibility problems with methacrylate bonding adhesives and cements when used together. Epoxy/(meth)acrylate containing compounds containing both epoxy and (meth)acrylate functionality are also known and are obtained from reaction of multi-epoxide containing compound with one or less equivalent of (meth)acrylic acid, or reaction of hydroxyl containing (meth)acrylate with epichlorohydrin. Commercially available epoxy/methacrylate include 3,4-epoxy-cyclohexyl methyl methacrylate from Daicel Chemical, Japan. U.S. Pat. No. 6,187,833 to Oxman et al. generally discloses photocurable compositions containing an epoxy resin, a hydroxyl-containing material, and optionally a free radically polymerizable material. The compositions contain a ternary photoinitiator system comprising an iodonium salt, a visible light sensitizer, and an electron donor compound. Oxman et al. disclose a bifunctional epoxy/acrylate material, but do not disclose an epoxy/acrylate oligomeric material made from the reaction product of a multi-epoxide containing compound and hydroxy (meth)acrylate.
Alternative fillers for restorative dental resin materials have also been developed. Current fillers are glasses, occasionally glass-ceramics and quartz (a crystalline form of silica), particulate polymers and glass-polymer composite particulates. Hybrid filler systems have been developed, based on fillers having an average particle size of 0.6 micrometers or greater in combination with a microfiller having an average particle size of about 0.05 micrometers or less.
Most prior art composite dental restorative materials are intended for permanent dental restorations. The combination of resin and filler are therefore selected to have the desired aesthetic properties, as well as physical properties such a high hardness, low water absorption, low shrinkage, and the like. Composites for temporary dental restorations, on the other hand, have less stringent aesthetic considerations and require slightly different physical properties, including ease of placement and removability. Temporary dental materials thus often have a dull finish that does not blend with natural dentition. The practitioner may also spend less time on surface finishing or polishing because the temporary nature of the restoration.
There accordingly remains a need in the art for dental sealants and glazes that are suitable for use with permanent or temporary composite materials, that are easy to apply, and that will enhance the aesthetic appearance of temporary dental composite restorations.